THURSDAY, Sept. 29 (HealthDay News) -- Working rotating shifts is not as potentially unhealthy as it used to be, according to new Canadian research that suggests modern shift patterns may not carry the same risks for cancer as older, more extreme shift schedules.

"Recent research has suggested shift work could increase the risk of cancer, although the biological mechanism responsible for this observation is still unknown," the study's lead author, Anne Grundy, a doctoral student in the Queen's University department of community health and epidemiology in Ontario, said in a university news release. "Our study indicates that the now common rotating shift pattern of day-day-night-night may not disrupt circadian rhythm or melatonin production significantly."

Melatonin, a hormone shown to have anti-carcinogenic qualities, is tied to the light-dark cycle, and melatonin levels typically peak between midnight and 4 a.m. As a result, shift workers who are exposed to light throughout the night may have an increased risk of diseases such as cancer. The study found, however, that recent changes in how shifts are scheduled may help reduce the health risks for these workers.

The researchers studied 123 Kingston General Hospital shift workers who wore light-intensity meters to determine their peak melatonin levels and the overall change in melatonin levels during winter day and night shifts, as well as summer day and night shifts.

In the hospital where the study took place, the wards are dimly lit at night, resulting in little difference in peak melatonin levels between day- and night-shift workers. In cases where the night workers were exposed to more light, however, the workers' overall change in melatonin levels decreased slightly, which the study authors called a statistically significant finding.

"We've already seen a shift away from the older patterns of two weeks of days, two weeks of nights and a short time off, to more humane patterns of day-day-night-night then five days off, so it's possible that an intervention to combat the health risks of shift work has already occurred," Grundy said in the news release.

"However, the overall change in melatonin levels that we found may still be a concern," she added. "We look forward to seeing other studies that either confirm our findings or that examine the impact of specific risk factors like extreme shift patterns and higher intensities of light at night."

The findings were published in the Sept. 27 online edition of Cancer Epidemiology, Biomarkers & Prevention.